An internal milling cutter is an annular milling cutter on the inner periphery of which are arranged several cutting edges, which are generally provided on interchangeable cutting inserts. For the machining of the workpiece, the rotating ring is moved in space such that the inner periphery of the ring, in that region of the workpiece which is to be machined, is moved radially inward to enable the cutting edges to cut a recess in the workpiece.
Internal milling cutters are used in the manufacture of crankshafts, for instance, for machining of the bearing seats. Both the seats for the main bearings and those for the pin bearings can be machined. Internal milling cutters are here used, for instance for roughing, in order to remove excess material to essentially the final desired measures.
In the case of eccentrically mounted workpieces, for instance the pin bearings of a crankshaft, the internal milling cutter, in addition to its spinning about the center point of the milling cutter, which spinning is necessary to generate the cutting force, can also move in a circular path about the workpiece in order to machine the latter on the whole of its periphery. With an appropriate control system, it is possible also to make the workpiece rotate in an eccentric motion in order to aid the milling process.
To the inner periphery of the milling cutter are generally attached several groups of interchangeable cutting inserts. For the production of a specific axial portion, each of the interchangeable cutting inserts is assigned to the recess cut into the workpiece by the milling cutter.
In FIGS. 1 and 2, this is represented for an internal milling cutter known from the prior art. FIG. 1 shows a portion of a tool holder of the internal milling cutter, which portion is equipped with a group of interchangeable cutting inserts A-D which produces the periphery cut into the workpiece and represented in FIG. 2 (see line S).
The group of cutting inserts A D which is shown in FIG. 1 is repeated in identical assembly and orientation along the periphery of the milling cutter. The exact number of cutting inserts in such a group, and the number of groups over the periphery of the milling cutter, are dependent, of course, on the workpiece to be machined and, in particular, on the dimensions of the internal milling cutter.
The peripheral surface (shown in cross section in FIG. 2) which is cut into the workpiece by the milling cutter and has the peripheral line L is obtained by assembly of the cutting edges of the group of interchangeable cutting inserts A D from FIG. 1, viewed in the peripheral direction of the tool holder. In FIG. 2, all the cutting inserts A D are rotated diagrammatically from their axial position into a radial plane. The assembled sectional line of all interchangeable cutting inserts of the shown group is thereby discernible.
In FIG. 2 it can be seen that the recess produced by the internal milling cutter terminates on both sides, corresponding to the peripheral margins of the internal milling cutter, in a radius of defined curvature. This radius is produced by the interplay of a plurality of interchangeable cutting inserts A, B, C. In this case, the radius is respectively cut by cutting edges on three individual cutting inserts A, B, C. When the tool is advanced in the radial direction in the direction of cut S, the interchangeable cutting insert A, for instance, first comes into contact with the workpiece, then the laterally outer cutting edge of the interchangeable cutting insert B, and finally the laterally outer cutting edge of the interchangeable cutting insert C. The contour L shown in FIG. 1 for the radius is cut by the interchangeable cutting inserts in combination.
The radius is in this case identical on both peripheral sides of the internal milling cutter, but is configured, of course, in mirror image.
All three interchangeable cutting inserts A, B, C are configured differently in terms of their geometry and size. Three different types of interchangeable cutting inserts are thus used solely to produce the radius.
That portion of the line cut into the workpiece by the internal milling cutter which lies between the two radii is produced by five interchangeable cutting inserts D of a further type, which in turn have a different form than the interchangeable cutting inserts A, B and C.